1. Field of the Invention
The present invention relates to a communication method in which, using a plurality of communication devices and a relaying device that relays data transmissions between the communication devices, one of the communication devices transmits a transmission right request to the relaying device and transmits data to the relaying device when a transmission right is granted by the relaying device, and the relaying device broadcasts the received data to other communication devices, and further relates to a communication system employing the communication method, as well as to the relaying device provided for the communication system, and the communication device provided for the communication system. In particular, the invention relates to a communication method, a communication system, a relaying device and a communication device that are applicable to a PoC (Push-to-Talk over Cellular) service whereby data is transmitted to a plurality of devices by multiple addressing, by using IP (Internet Protocol) telephone in the same manner as in communication between transceivers.
2. Description of the Related Art
At present, use of real-time application such as VoIP (Voice over Internet Protocol), VoPN (Voice over Packet Network), streaming delivery, etc. has been increasing, wherein voice and image data is transmitted and received among communication devices by way of a communication network such as IP (Internet Protocol) network. Then, an IP telephone, one example thereof, has been spreading rapidly. IP telephony implements a call between a communication device on a transmitting end and that on a receiving end by transmitting/receiving voice data by way of an IP network.
In addition, a service called PoC (Push-to-Talk over Cellular) has now come under the spotlight wherein it transmits packets containing voice data to a plurality of communication devices by multiple addressing, by using technology of the IP telephone as if it were a transceiver. The characteristic of the PoC service is that the PoC employs half duplex communication wherein one of a plurality of communication devices acquires a transmission right to transmit voice data, the one communication device that has acquires the transmission right transmits the voice data to the other plurality of communication devices by multiple addressing, and thus enabling the simultaneous communication among three or more devices.
As described above, in a group communication system such as the PoC service, etc, one device that has acquired a transmission right transmits voice data to a plurality of other devices by using multiple addressing, which can realize a one-to-many communication, thereby saving trouble and reducing cost of transmitting the same content individually. As another advantage, even if a speaker who has acquired the transmission right intends to speak to a single person, it is possible to share the information by broadcasting the content.
Further, Japanese Published Patent Publication No. 2003-526276 also discloses an embodiment in which a digital camera, for example, is used as a communication device in such a service.